CN115987335A

CN115987335A - Distributed multi-user (MU) wireless communication

Info

Publication number: CN115987335A
Application number: CN202310021648.6A
Authority: CN
Inventors: S·韦玛尼; B·田
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 2017-02-15
Filing date: 2018-01-17
Publication date: 2023-04-18
Also published as: US20210226671A1; US11728848B2; US20240022286A1; KR20190116308A; SG11201905921PA; CA3049131A1; BR112019016747A2; KR102230693B1; WO2018151888A1; CN110291724A; KR102406456B1; CA3049131C; EP3583702A1; US10897285B2; EP3583702B1; KR20210031797A; CN110291724B; US20180234135A1

Abstract

The present disclosure relates to distributed multi-user (MU) wireless communications. Systems, methods, and apparatus, including computer programs encoded on a computer storage medium, for group formation and sounding for distributed multi-user multiple-input multiple-output (MU-MIMO) are provided. Some implementations include a method of wireless communication. The method comprises the following steps: an announcement frame is transmitted from a first access point of the plurality of access points for performing a beamforming procedure for distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from a basic service set of the first access point.

Description

Distributed multi-user (MU) wireless communication

The application is a divisional application of patent applications with international application date of 2018, 1 month and 17 days, international application numbers of PCT/US2018/013943 and Chinese application numbers of 201880011682.2 and the name of invention of distributed multi-user (MU) wireless communication.

Cross Reference to Related Applications

This application claims priority from U.S. application No.15/872,294 filed on day 1, month 16, 2018, which claims benefit from U.S. provisional patent application S/n.62/459,290 filed on day 15, month 2, 2017. The contents of both applications are incorporated herein by reference in their entirety.

Technical Field

The present disclosure relates generally to wireless communications, and more particularly to systems and methods for group formation and sounding for distributed multi-user multiple-input multiple-output (MU-MIMO).

Description of the related Art

To address the increasing bandwidth requirements required for wireless communication systems, different schemes are being developed to allow multiple user terminals to communicate with a single Access Point (AP) or multiple APs by sharing channel resources while achieving high data throughput. Multiple-input multiple-output (MIMO) technology represents one such approach, which is a recently emerging popular technique for next generation communication systems.

MIMO systems employing multiple (N) _T Multiple (N) transmitting antennas and multiple (N) _R And) receiving antennas for data transmission. From this N _T A transmitting antenna and N _R A MIMO channel composed of multiple receiving antennas can be decomposed into N _S Independent channels, also called spatial channels, in which N _S ≤min{N _T ,N _R }. This N _S Each of the individual channels corresponds to a dimension. The MIMO system can provide improved performance (such as higher throughput and greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.

In a wireless network with multiple APs and multiple user Stations (STAs), concurrent transmissions may occur on multiple channels (in both the uplink and downlink directions) to different STAs. There are many challenges in such systems. For example, the AP may transmit signals using different standards, such as IEEE802.11 n/a/b/g or IEEE802.11ac (very high throughput (VHT)) standards. The receiver STA may be able to detect the transmission mode of the signal based on information included in the preamble of the transmission packet.

A downlink multi-user MIMO (MU-MIMO) system based on Spatial Division Multiple Access (SDMA) transmission can simultaneously serve multiple spatially separated STAs by applying beamforming at an antenna array of an AP. The complex transmit precoding weights may be calculated by the AP based on Channel State Information (CSI) received from each of the supported STAs.

In a distributed MU-MIMO system, multiple APs may simultaneously serve multiple spatially separated STAs by coordinating beamforming by the antennas of the multiple APs. For example, multiple APs may coordinate transmissions to each STA.

SUMMARY

The systems, methods, and apparatus of the present disclosure each have several inventive aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosure can be implemented in a method of wireless communication. The method comprises the following steps: an announcement frame is transmitted from a first access point of the plurality of access points for performing a beamforming procedure for distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from a basic service set of the first access point. The method further comprises the following steps: a packet for measuring a channel is transmitted from the first access point. The method further comprises the following steps: receiving, by the first access point, feedback information from the user terminal based on the packet for measuring the channel. The method further comprises the following steps: transmitting, by the first access point, the distributed transmission using the beamforming procedure. The beamforming procedure is based on the feedback information.

Another innovative aspect of the subject matter described in this disclosure can be implemented in a first access point of a plurality of access points. The first access point includes a memory and a processor coupled to the memory. The processor is configured to transmit an announcement frame for performing a beamforming procedure for a distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from a basic service set of the first access point. The processor is further configured to transmit a packet for measuring a channel. The processor is further configured to receive feedback information from the user terminal based on the packet for measuring channels. The processor is further configured to transmit the distributed transmission using the beamforming procedure. The beamforming procedure is based on the feedback information.

Another innovative aspect of the subject matter described in this disclosure can be implemented in a first access point of a plurality of access points. The apparatus includes means for transmitting an announcement frame for performing a beamforming procedure for a distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from a basic service set of the first access point. The first access point further includes means for transmitting a packet for measuring a channel. The first access point further comprises means for receiving feedback information from the user terminal based on the packet for measuring channels. The first access point further includes means for transmitting the distributed transmission using the beamforming procedure, wherein the beamforming procedure is based on the feedback information.

Another innovative aspect of the subject matter described in this disclosure can be embodied in a non-transitory computer-readable medium that, when executed by at least one processor, causes the at least one processor to perform a method of wireless communication. The method comprises the following steps: an announcement frame is transmitted from a first access point of the plurality of access points for performing a beamforming procedure for distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from a basic service set of the first access point. The method further comprises the following steps: a packet for measuring a channel is transmitted from the first access point. The method further comprises the following steps: receiving, by the first access point, feedback information from the user terminal based on the packet for measuring the channel. The method further comprises the following steps: transmitting, by the first access point, the distributed transmission using the beamforming procedure. The beamforming procedure is based on the feedback information.

In some implementations, the method or first access point may include: a group formation trigger for forming a group comprising a plurality of access points is transmitted from a first access point for performing a beamforming procedure for distributed transmission. The method or the first access point may further comprise: receiving an intent to participate from at least one of the plurality of access points based on the group formation trigger. The method or the first access point may further comprise: forming the group based on receiving the intent to participate from at least one of the plurality of access points.

In some implementations, the group formation trigger includes an indication of the number of spatial streams available for transmission by other access points.

In some implementations, the method or the first access point may include: transmitting, by the first access point, a request frame requesting the feedback information, wherein the request frame includes at least one identifier of a user terminal in a basic service set different from a basic service set of the first access point.

In some implementations, the announcement frame includes an allocation of a plurality of spatial streams to the plurality of access points.

In some implementations, each access point of the plurality transmits separate packets for measuring a channel during a first time interval based on the announcement frame, and the plurality of access points multiplexes transmitting the separate packets using one or more of frequency division multiplexing, code division multiplexing, P-matrix, or time division multiplexing.

In some implementations, each of the plurality of access points transmits separate packets for measuring the channel during different time intervals based on the announcement frame.

In some implementations, each access point of the plurality transmits a separate announcement frame based on the announcement frame transmitted by the first access point.

In some implementations, each access point of the plurality of access points transmits a separate packet for measuring a channel during a first time interval based on the announcement frame.

In some implementations, the method or first access point may include: transmitting, by the first access point, a request frame requesting the feedback information, wherein the request frame includes at least one identifier of a user terminal in a basic service set different from a basic service set of the first access point.

Another innovative aspect of the subject matter described in this disclosure can be implemented in a method of wireless communication. The method comprises the following steps: a group formation trigger for forming a group comprising a plurality of access points is transmitted from a first access point for performing a beamforming procedure for distributed transmission. The method further comprises the following steps: receiving an intent to participate from at least one of the plurality of access points based on the group formation trigger. The method further comprises the following steps: forming the group based on receiving the intent to participate from at least one of the plurality of access points.

Another innovative aspect of the subject matter described in this disclosure can be implemented in a first access point. The first access point includes a memory and a processor coupled to the memory. The processor is configured to transmit a group formation trigger for forming a group comprising a plurality of access points for performing a beamforming procedure for distributed transmission. The processor is further configured to receive an intent to participate from at least one access point of the plurality of access points based on the group formation trigger. The processor is further configured to form the group based on receiving the intent to participate from at least one of the plurality of access points.

Another innovative aspect of the subject matter described in this disclosure can be implemented in a first access point. The apparatus includes means for transmitting a group formation trigger for forming a group comprising a plurality of access points for performing a beamforming procedure for distributed transmission. The apparatus further includes means for receiving an intent to participate from at least one access point of the plurality of access points based on the group formation trigger. The first access point further includes means for forming the group based on receiving the intent to participate from at least one of the plurality of access points.

Another innovative aspect of the subject matter described in this disclosure can be embodied in a non-transitory computer-readable medium that, when executed by at least one processor, causes the at least one processor to perform a method of wireless communication. The method comprises the following steps: a group formation trigger for forming a group comprising a plurality of access points is transmitted from a first access point for performing a beamforming procedure for distributed transmission. The method further comprises the following steps: an intent to participate is received from at least one of the plurality of access points based on the group formation trigger. The method further comprises the following steps: forming the group based on receiving the intent to participate from at least one of the plurality of access points.

In some implementations, the method or first access point may include: wherein the group formation trigger includes an indication of a number of spatial streams available for transmission by other access points.

The details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. It should be noted that the relative dimensions of the following figures may not be drawn to scale.

Brief Description of Drawings

Fig. 1 illustrates an example wireless communication network.

Fig. 2 illustrates a block diagram of an example access point and user terminal.

Fig. 3 illustrates a block diagram of an example wireless device.

Fig. 4 illustrates an example of a distributed multi-user multiple-input multiple-output (MU-MIMO) system.

Fig. 5 illustrates a signal diagram of an example joint sounding procedure for distributed MU-MIMO.

Fig. 6 illustrates a signal diagram of an example sequential sounding procedure for distributed MU-MIMO.

Fig. 7 illustrates a signal diagram of an example over-the-air group formation procedure for distributed MU-MIMO.

Fig. 8 illustrates example operations for performing a sounding procedure for distributed MU-MIMO.

Fig. 9 illustrates example operations for performing an over-the-air group formation procedure for distributed MU-MIMO.

Like reference numbers and designations in the various drawings indicate like elements.

Detailed Description

The following description is directed to certain implementations to illustrate the innovative aspects of the present disclosure. However, one of ordinary skill in the art will readily recognize that the teachings herein may be applied in a number of different ways. The described implementations may be implemented in any device, system, or network capable of transmitting and receiving RF signals according to: any one of the IEEE16.11 standards or any one of the IEEE802.11 standards,

(Bluetooth) standard, code Division Multiple Access (CDMA), frequency Division Multiple Access (FDMA), time division multiple access (T)DMA), global system for mobile communications (GSM), GSM/General Packet Radio Service (GPRS), enhanced Data GSM Environment (EDGE), terrestrial trunked radio (TETRA), wideband CDMA (W-CDMA), evolution-data optimized (EV-DO), 1xEV-DO, EV-DO revision a, EV-DO revision B, high Speed Packet Access (HSPA), high Speed Downlink Packet Access (HSDPA), high Speed Uplink Packet Access (HSUPA), evolved high speed packet access (HSPA +), long Term Evolution (LTE), AMPS, or other known signals for communicating within a wireless network, cellular network, or internet of things (IOT) network, such as a system utilizing 3G, 4G, or 5G technology or further implemented thereof.

The techniques described herein may be used for various broadband wireless communication systems, including communication systems based on single carrier transmission. For example, aspects may be advantageous for systems employing ultra-wideband (UWB) signals including millimeter-wave signals. However, the present disclosure is not intended to be limited to such systems, as other encoded signals may benefit from similar advantages.

The various techniques may be incorporated into (such as implemented within or performed by) various wired or wireless devices (such as nodes). In some implementations, the node comprises a wireless node. Such wireless nodes may provide connectivity for or to a network, such as a Wide Area Network (WAN), such as the internet or a cellular network, for example, via wired or wireless communication links. In some implementations, a wireless node may comprise an access point or a user terminal.

Multiple APs may transmit to multiple recipient user terminals at a time by using distributed multi-user multiple-input multiple-output (MU-MIMO). For example, multiple APs may transmit data to a given user terminal at a time, meaning that data transmissions to the user terminal are distributed among the multiple APs. Multiple APs may utilize beamforming to spatially direct signals to user terminals. In some implementations, for multiple APs to perform distributed MU-MIMO, the multiple APs coordinate beamforming performed by each AP to reduce interference to transmitting data to user terminals. In some implementations, multiple APs perform procedures for forming a group of APs to transmit to a user terminal, as discussed herein. Further, in some implementations, to coordinate beamforming between multiple APs, the multiple APs perform a sounding procedure to collect feedback information from a user terminal regarding wireless channels between the multiple APs and the user terminal, as discussed herein. The plurality of APs may perform beamforming using the feedback information.

Particular implementations of the subject matter described in this disclosure can be implemented to achieve one or more of the following potential advantages. For example, the APs may form a group for transmitting to user terminals using over-the-air signaling, rather than communicating over the backhaul. This may reduce data congestion on the backhaul. Additionally, the sounding schedule may allow feedback information to be collected from the user terminal by multiple APs in coordination. Accordingly, feedback information for multiple APs may include channel conditions for each of the multiple APs coordinated in time, which may improve accuracy of beamforming based on the feedback information. Further, the sounding schedule may limit the amount of data exchanged wirelessly to perform the sounding schedule, which may reduce bandwidth usage of the wireless channel.

Fig. 1 illustrates a multiple-access multiple-input multiple-output (MIMO) system 100 with an access point and user terminals. For simplicity, only one access point 110 is shown in fig. 1. An Access Point (AP) is generally a fixed station that communicates with the user terminals and may be referred to as a base station or some other terminology. A user terminal may be fixed or mobile and may be referred to as a mobile station, a Station (STA), a client, a wireless device, or some other terminology. The user terminal may be a wireless device such as a cellular telephone, personal Digital Assistant (PDA), handheld device, wireless modem, laptop computer, personal computer, or the like.

Access point 110 may communicate with one or more user terminals 120 on the downlink and uplink at any given moment. The downlink (i.e., forward link) is the communication link from the access points to the user terminals, and the uplink (i.e., reverse link) is the communication link from the user terminals to the access points. A user terminal may also communicate peer-to-peer with another user terminal. A system controller 130 couples to and provides coordination and control for the access points.

MIMO system 100 employs multiple transmit antennas and multiple receive antennas for data transmission on the downlink and uplink. The access point 110 is equipped with a number N _ap Multiple antennas and for downlink transmission Multiple Input (MI) and for uplink transmission Multiple Output (MO). Set N of selected user terminals 120 _u Collectively representing multiple outputs for downlink transmissions and multiple inputs for uplink transmissions. In some implementations, if used for this N _u Where the data symbol streams for individual user terminals are not multiplexed in code, frequency, or time by some means, then it is desirable to have N _ap ≥N _u Not less than 1. N if the data symbol streams can be multiplexed using different code channels in CDMA, disjoint sets of subbands in OFDM, etc _u May be greater than N _ap . Each selected user terminal transmits user-specific data to and receives user-specific data from the access point. In general, each selected user terminal may be equipped with one or more antennas (i.e., N) _ut Not less than 1). This N _u The selected user terminals may have the same or different numbers of antennas.

MIMO system 100 may be a Time Division Duplex (TDD) system or a Frequency Division Duplex (FDD) system. For a TDD system, the downlink and uplink share the same frequency band. For FDD systems, the downlink and uplink use different frequency bands. MIMO system 100 may also utilize a single carrier (such as a carrier frequency) or multiple carriers for transmission. Each user terminal may be equipped with a single antenna (such as to keep costs down) or multiple antennas (such as where additional costs can be supported). MIMO system 100 may represent a high-speed Wireless Local Area Network (WLAN) operating in the 60GHz band.

Fig. 2 shows a block diagram of an access point/base station 110 and two user terminals/

user equipments

120m and 120x in a MIMO system 100. The access point 110 is equipped with N _ap And antennas 224a through 224ap. User terminal 120m is equipped with N _ut,m Antennas 252ma through 252mu, and user terminal 120x is equipped with N _ut,x And antennas 252xa through 252xu. The access point 110 is the transmitting entity for the downlink andand in the uplink is the receiver entity. Each user terminal 120 is a transmitting entity for the uplink and a receiving entity for the downlink. As used herein, a "transmitting entity" is a separately operating device or apparatus capable of transmitting data via a frequency channel, while a "receiving entity" is a separately operating device or apparatus capable of receiving data via a frequency channel. In the following description, the subscript "dn" denotes the downlink, the subscript "up" denotes the uplink, N _up Several user terminals are selected for simultaneous transmission on the uplink, and N _dn The user terminals are selected for simultaneous transmission on the downlink. Furthermore, N _up May or may not be equal to N _dn And N is _up And N _dn May include a static value or may change for each scheduling interval. Beamforming (such as beam steering) or some other spatial processing technique may be used at the access point and the user terminal.

On the uplink, at each user terminal 120 selected for uplink transmission, a TX data processor 288 receives traffic data from a data source 286 and control data from a controller 280. TX data processor 288 processes (e.g., encodes, interleaves, and modulates) the traffic data for the user terminal { d } based on the coding and modulation schemes associated with the rate selected for the user terminal _up,m And provides a stream of data symbols, { s } _up,m }. TX spatial processor 290 processes the data symbol stream s _up,m Performs spatial processing and provides it to N _ut,m N of one antenna _ut,m A stream of transmit symbols. Each transmitter unit (TMTR) 254 receives and processes (e.g., converts to analog, amplifies, filters, and frequency upconverts) a respective transmit symbol stream to generate an uplink signal. N is a radical of _ut,m A transmitter unit 254 providing N _ut,m An uplink signal to carry out a slave N _ut,m Transmission of antenna 252 to access point 110.

Number N _up The user terminals may be scheduled for simultaneous transmission on the uplink. Each of these user terminals performs spatial processing on its data symbol stream and transmits on the uplink to the access pointIt is sent to transmit the set of symbol streams.

At access point 110, N _ap Multiple antennas 224a through 224ap from all N transmitting on the uplink _up Each user terminal receives an uplink signal. Each antenna 224 provides a received signal to a respective receiver unit (RCVR) 222. Each receiver unit 222 performs processing complementary to that performed by transmitter unit 254 and provides a received symbol stream. RX spatial processor 240 pairs data from N _ap N of a receiver unit 222 _ap Receiver spatial processing of received symbol streams and providing N _up A stream of recovered uplink data symbols. Receiver spatial processing is performed based on Channel Correlation Matrix Inversion (CCMI), minimum Mean Square Error (MMSE), successive Interference Cancellation (SIC), or some other technique. Each recovered uplink data symbol stream s _up,m Is a function of the data symbol stream s transmitted by the respective corresponding user terminal _up,m An estimate of. RX data processor 242 can determine the number of symbols used for each recovered uplink data symbol stream s _up,m Processing (such as demodulating, deinterleaving, and decoding) the recovered stream of uplink data symbols, { s }, at a rate _up,m To obtain decoded data. The decoded data for each user terminal may be provided to a data sink 244 for storage and/or to the controller 230 for further processing.

On the downlink, at access point 110, a TX data processor 210 receives N scheduled for downlink transmission from a data source 208 _dn Traffic data for individual user terminals, control data from controller 230, and possibly other data from scheduler 234. Various types of data may be sent on different transport channels. TX data processor 210 processes (e.g., encodes, interleaves, and modulates) the traffic data for each user terminal based on a rate selected for that user terminal. TX data processor 210 is N _dn Individual user terminal providing N _dn A stream of downlink data symbols. TX spatial processor 220 pairs N _dn Performing spatial processing on one downlink data symbol stream and for N _ap One antenna provides N _ap A stream of transmit symbols. Each transmitterA unit (TMTR) 222 receives and processes a respective transmit symbol stream to generate a downlink signal. N is a radical of _ap A transmitter unit 222 providing N _ap A downlink signal for the slave N _ap Each antenna 224 is transmitted to a user terminal.

At each user terminal 120, N _ut,m N received by antennas 252 from access point 110 _ap A downlink signal. Each receiver unit (RCVR) 254 processes a received signal from an associated antenna 252 and provides a received symbol stream. RX spatial processor 260 on the data from N _ut,m N of one receiver unit 254 _ut,m Performs receiver spatial processing on each received symbol stream and provides a recovered downlink data symbol stream s for the user terminal 120 _dn,m }. Receiver spatial processing may be performed in accordance with CCMI, MMSE, or other known techniques. An RX data processor 270 processes (e.g., demodulates, deinterleaves, and decodes) the recovered downlink data symbol stream to obtain decoded data for the user terminal.

At each user terminal 120, N _ut,m N received by antennas 252 from access point 110 _ap A downlink signal. Each receiver unit (RCVR) 254 processes a received signal from an associated antenna 252 and provides a stream of received symbols. RX spatial processor 260 on the data from N _ut,m N of one receiver unit 254 _ut,m Performing receiver spatial processing on each received symbol stream and providing a recovered downlink data symbol stream { s } for the user terminal _dn,m }. The receiver spatial processing is performed in accordance with CCMI, MMSE, or some other technique. An RX data processor 270 processes (e.g., demodulates, deinterleaves, and decodes) the recovered downlink data symbol stream to obtain decoded data for the user terminal.

Fig. 3 illustrates various components that may be utilized in a wireless device 302 that may be employed within the MIMO system 100. The wireless device 302 is an example of a device that may be configured to implement the various methods described herein. The wireless device 302 may be an access point 110 or a user terminal 120.

The wireless device 302 may include a processor 304 that controls the operation of the wireless device 302. The processor 304 may also be referred to as a Central Processing Unit (CPU). Memory 306, which may include both read-only memory (ROM) and Random Access Memory (RAM), provides instructions and data to the processor 304. A portion of the memory 306 may also include non-volatile random access memory (NVRAM). The processor 304 typically performs logical and arithmetic operations based on program instructions stored within the memory 306. The instructions in memory 306 may be executable to implement methods or operations described herein (such as those described with respect to fig. 8 or 9).

The wireless device 302 may also include a housing 308, which housing 308 may include a transmitter 310 and a receiver 312 to allow transmission and reception of data between the wireless device 302 and a remote location. The transmitter 310 and receiver 312 may be combined into a transceiver 314. A plurality of transmit antennas 316 may be attached to the housing 308 and electrically coupled to the transceiver 314. The wireless device 302 may also include (not shown) multiple transmitters, multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that may be used to detect and quantify the level of signals received by the transceiver 314. The signal detector 318 may detect signals such as total energy, energy per subcarrier per symbol, power spectral density, and other signals. The wireless device 302 may also include a Digital Signal Processor (DSP) 320 for use in processing signals.

The various components of the wireless device 302 may be coupled together by a bus system 322, which bus system 322 may include a power bus, a control signal bus, and a status signal bus in addition to a data bus.

Distributed MU-MIMO

As discussed with respect to fig. 1-3, a single AP110 may transmit to multiple recipient user terminals 120 at a time by using multi-user MIMO (MU-MIMO). The AP110 includes multiple antennas 224. By using multiple antennas 224, the ap110 may utilize beamforming to spatially focus the energy of the transmitted signal (such as to the user terminal 120 as a spatial stream). To perform beamforming, the AP110 may exchange frames with the user terminal 120 to measure a channel between the AP110 and the user terminal 120. For example, the AP110 may transmit a Null Data Packet (NDP) that includes one or more Long Training Fields (LTFs) used by the user terminals 120 to measure the channel. The user terminal 120 may generate channel feedback information (such as a feedback matrix) based on the channel measurements and transmit the feedback matrix to the AP 110. Using the feedback matrix, the AP110 may derive a steering matrix that the AP110 uses to determine how to transmit signals on each antenna 224 of the AP110 to perform beamforming. For example, the steering matrix may indicate phase shifts, power levels, etc. for transmitting signals on each antenna 224. For example, AP110 may be configured to perform similar beamforming techniques as described in the 802.11ac standard.

In some implementations, multiple APs 110 may be configured to utilize distributed MU-MIMO to transmit to one or more recipient user terminals 120 at a time. There may be a number of different types of MU-MIMO transmission, including coordinated beamforming (COBF) and joint processing transmission (JT).

Fig. 4 illustrates a distributed MU-MIMO system 400. As shown, system 400 includes AP110a and AP110 b. In some implementations,

APs

110a and 110b refer to AP110 described with respect to fig. 1. AP110a is shown as part of a first Basic Service Set (BSS), namely BSS1, and AP110b is shown as part of a second BSS, namely BSS 2. AP110a and AP110b may be neighboring APs. Further, a portion of the coverage area of the AP110a may overlap with a portion of the coverage area of BSS2, resulting in an Overlapping BSS (OBSS) situation. The communication by the AP110a with the user terminal in the BSS1 may be referred to as BSS communication. Similarly, the communication by the AP110b with the user terminal in the BSS2 may be referred to as BSS communication. Further, communication by the AP110a with the user terminal in the BSS2 may be referred to as OBSS communication, and communication by the AP110b with the user terminal in the BSS1 may be referred to as OBSS communication.

In COBF, signals (such as data) for a given user terminal may be transmitted by only a single AP. For example,

user terminals

120a and 120b are shown as part of BSS1, so only AP110a may transmit signals intended for

user terminals

120a and 120 b. Further,

user terminals

120c and 120d are shown as part of BSS2, so only AP110b may transmit signals intended for

user terminals

120c and 120d. In some implementations, the user terminals 120 a-120 d refer to the user terminals 120 described with respect to fig. 1. However, as discussed, the coverage areas of AP110a and AP110b may overlap, and thus the signals transmitted by AP110a may reach

user terminals

120c and 120d in BSS2 as OBSS signals. Similarly, the signal transmitted by AP110b may arrive as an OBSS signal to

user terminals

120a and 120d in BSS 1. In COBF,

APs

110a and 110b may be configured to perform beamforming to form null (null) in the direction of a user terminal in an OBSS, such that any signal received at the OBSS user terminal has low power. For example, AP110a may be configured to perform beamforming to form nulls towards

user terminals

120c and 120d, and AP110b may be configured to form nulls towards

user terminals

120a and 120b to limit interference at the user terminals. Accordingly, in COBF, the AP is configured to form null for OBSS user terminals and to beamform signals to user terminals within the BSS.

In JT, signals for a given user terminal may be transmitted by multiple APs. For example, one or more of the user terminals 120 a-120 d may receive signals from both AP110a and AP110 b. For multiple APs to transmit data to a user terminal, the multiple APs may all need a copy of the data to be transmitted to the user terminal. Accordingly, the APs may need to exchange data between each other (such as over a backhaul) for transmission to the user terminal. For example, AP110a may have data to transmit to user terminal 120a, and may further communicate the data to AP110b over a backhaul. The AP110a and the AP110b may then beamform the signal including the data to the user terminal 120 a.

In some implementations, the antennas of multiple APs transmitting to one or more user terminals in JT may be considered one large antenna array (such as a virtual antenna array) for beamforming and transmitting signals. Accordingly, similar beamforming techniques as discussed and used for transmitting from multiple antennas of a single AP to one or more user terminals may instead be used for transmitting from multiple antennas of multiple APs. For example, the same beamforming to compute steering matrices, etc., for transmitting from multiple antennas of AP110a may be applied to transmit from multiple antennas of both AP110a and AP110 b. Multiple antennas of multiple APs may be capable of forming signals on multiple spatial streams (such as limited by the number of antennas). Accordingly, each user terminal may receive signals on one or more of the plurality of spatial streams. In some implementations, each AP may be assigned a particular number of the plurality of spatial streams for transmitting to user terminals in the BSS of the AP. Each spatial stream may be identified by a spatial stream index.

In some implementations, various factors may affect distributed MU-MIMO. For example, one factor may be channel feedback accuracy. As discussed, to perform beamforming, each AP may exchange signals with each user terminal over a communication channel, and each user terminal may measure the channel based on the exchanged signals. Each user terminal may further transmit information on channel measurement as channel feedback information to each AP. Each AP may perform beamforming using the channel feedback information. However, channel conditions may change between when each AP receives channel feedback information and when each AP transmits a signal on the channel. This may be referred to as channel aging. Furthermore, there may be inaccuracies due to the quantization of the information included in the channel feedback information. This may affect both COBF and JT distributed MU-MIMO and cause leakage and interference.

Another factor may be the phase offset between APs. For example, APs may transmit at different phases due to timing synchronization differences between APs. Furthermore, the phase difference may drift or change (such as due to phase noise, timing drift, carrier Frequency Offset (CFO) drift, etc.) between when the channel feedback information is received and when each AP transmits to each user terminal. Such a change in phase difference may not significantly affect COBF because each AP independently performs beamforming. However, such a change in phase difference may affect JT because APs perform beamforming together.

Another factor may be timing offset. For example, the delay spread, filter delay, and arrival time spread of each AP using JT and COBF may need to be centered on the Cyclic Prefix (CP). Additionally, for JT, the relative timing offset (i.e., the change in timing offset between when the channel feedback information is measured and when the signal is transmitted) may also affect the phase offset and may need to be further controlled.

Another factor may be CFO. In COBF, the synchronization requirements for CFO may be reduced compared to JT.

Another factor may be gain mismatch, where different APs use different gain states when measuring the channel of the user terminal. This may have a greater effect on JT than on COBF. In some implementations of COBF, the maximum gain may be approximately 75% of the minimum of the number of transmit antennas of any AP. In some implementations of JT, the maximum gain may be about 75% of the sum of the transmit antennas of all APs.

In some implementations, in MU-MIMO, where a single AP transmits to multiple user terminals, to perform channel measurements for beamforming, all transmit antennas of the AP are probed together, meaning that all transmit antennas transmit NDPs during the same transmission time interval (such as TTI, frame, subframe, etc.). All antennas may be sounded together because if the NDP for each antenna is transmitted at a different TTI, they may be transmitted with different phases, and the receiver automatic gain control (RxAGC) at each user terminal receiving these NDPs, which may affect the gain applied to the received signal, may be different for different TTIs, which may make it difficult to stitch together measurements from different NDPs. Further, the relative timing between all transmit antennas used to transmit the NDP at the same TTI (such as relative to the start of the TTI) is constant for all transmit antennas and remains the same for when the NDP is transmitted and for when data is later transmitted to the user terminal based on the channel feedback information. Therefore, there is no change in relative timing between the NDP transmission and the data transmission, thereby ensuring better beamforming.

In some implementations, all antennas for multiple APs may be probed together to transmit NDP together at the same TTI for JT in a joint sounding schedule, avoiding the problems discussed. In some implementations, NDPs of different APs may be probed at the same TTI using one or more techniques, such as Time Division Multiplexing (TDM), code Division Multiplexing (CDM), such as using a P-matrix, and Frequency Division Multiplexing (FDM).

For COBF, the beamforming direction of one AP does not depend on the channel between the user terminal and the other APs. Accordingly, only loose synchronization may be required between APs. Thus, for COBF, in addition to being able to use a joint sounding procedure, a sequential sounding procedure may be used in which APs sound one at a time in separate TTIs and transmit NDPs at different TTIs per AP.

Fig. 5 illustrates a signal diagram of an example joint sounding procedure for distributed MU-MIMO. As shown, three APs (i.e., AP110a, AP110b, and AP110 c) may coordinate to perform distributed MU-MIMO transmission to two user terminals (i.e., user terminal 120a and user terminal 120 c). In some implementations, the APs 110a to 110c and the

user terminals

120a and 120c refer to the AP110 and the user terminal 120 described with respect to fig. 1. It should be noted, however, that distributed MU-MIMO transmissions may be made from any number of APs to any number of one or more user terminals. In this signal diagram, time is shown increasing along the x-axis. Initially, any one of the APs, here shown as AP110a, transmits an NDP announcement (NDPA) frame. The NDPA may be a control frame indicating that the NDP is to be transmitted. In some implementations, the NDPA includes information identifying one or more user terminals 120 to which the upcoming NDP is directed, so the one or more user terminals receiving the NDPA are aware to listen to the NDP to perform channel measurements. Accordingly, in this example, the NDPA may include identifiers of the user terminal 120a and the user terminal 120 c. Since the NDPA sent from AP110a may identify user terminals 120 associated with other APs, the NDPA may identify user terminals in the BSS of AP110a and the OBSS of AP110 a.

In some implementations, the NDPA may include allocation information for spatial streams of the AP 110. For example, the allocation information may include a mapping or correlation of spatial stream indices to the APs 110. The allocation of a spatial stream to a particular AP110 may indicate that the spatial stream is to be used for transmission in the BSS of the particular AP 110.

In some implementations, the NDPA may include allocation information for spatial streams of the user terminal 120. For example, the allocation information may include a mapping or correlation of spatial stream indices to user terminals 120. The allocation of a spatial stream to a user terminal 120 may indicate that the spatial stream is to be used for transmission to that user terminal 120.

In some implementations, the NDPA may include an identification (such as a BSS ID, MAC address, etc.) of the AP110 (APs 110a-110c in this example) that is to participate in the joint sounding procedure.

After the AP110a transmits the NDPA, each of the APs 110a-110c transmits the NDP at the same time (such as during the same TTI). In some implementations, the APs 110a-110c synchronize the transmission of the NDP based on the NDPA. For example, each AP110 a-110c may be configured to transmit the NDP after a fixed time interval, such as a short inter-frame space (SIFS), after receiving the NDPA. In some implementations, the APs 110a-110c synchronize the transmission of the NDP via the backhaul. The

user terminals

120a and 120c may receive the respective NDPs.

In some implementations, the NDPs are multiplexed to avoid interfering with each other. Specifically, each LTF from each NDP of multiple APs may be multiplexed. In some implementations, LTFs are multiplexed across APs using FDM. Further, in some implementations, each spatial stream belonging to each AP is multiplexed using FDM. For example, if there are N + M + X spatial streams, N belonging to AP110a, and M belonging to AP110b, and X belonging to AP110 c, then each N + M + X stream is transmitted on a different tone of each symbol on which the LTF is transmitted. Further, LTFs are transmitted over N + M + X symbols. Thus, each stream is transmitted on each tone. Thus, each stream for each AP may be estimated on each tone.

In some implementations, the NDPs are multiplexed using FDM and P matrices. In some implementations, the P matrix is an orthogonal code, where one dimension is the spatial stream and the other dimension is the LTF symbol. Accordingly, in some implementations, the spatial streams of individual APs 110 are multiplexed using a P matrix, but different APs 110 transmit on non-overlapping tones for each LTF symbol. Further, the LTFs are transmitted on enough symbols for each AP to transmit on each tone.

In some implementations, NDPs are multiplexed using only the P matrix. Specifically, the P matrix may have a size that accommodates all spatial streams for all APs 110.

In some implementations, NDP is multiplexed using TDM only, where each spatial stream is allocated to one LTF symbol and transmitted on all tones of the LTF symbol.

In some implementations, the NDPs are multiplexed using TDM and P matrices. Accordingly, in some implementations, the spatial streams of individual APs 110 are multiplexed using a P matrix, but different APs 110 transmit on different LTF symbols (such as all tones of an LTF symbol).

Further, after the APs 110a to 110c transmit the NDP, one of the APs, such as the AP110a, transmits a trigger request for feedback, such as channel feedback information, from each of the

user terminals

120a and 120c to which the NDP is transmitted. For example, the trigger request may be transmitted after a fixed period of time (such as SIFS) after the NDP is transmitted. Thus, the trigger request from AP110a may include the identifiers of

user terminals

120a and 120 c. Since the trigger request sent from AP110a may identify user terminals 120 associated with other APs, the trigger request may identify user terminals in the BSS of AP110a and the OBSS of AP110 a.

The

user terminals

120a and 120c identified in the trigger request may send channel feedback information to the AP110a based on the trigger request. As shown, the user terminals 120 may transmit channel feedback information in parallel (such as using uplink orthogonal frequency division multiple access (UL-OFDMA), UL MU-MIMO, etc.). However, in some implementations, the user terminal may transmit the feedback information serially (such as sequentially). In some implementations, instead of the AP110a sending a single trigger request for multiple user terminals, the AP110a may send multiple trigger requests (such as sequentially), one for each user terminal.

Further, as discussed, the remaining APs 110b and 110c may transmit trigger requests and receive feedback from the

user terminals

120a and 120 c. As shown, each AP110 separately transmits trigger requests and receives feedback information. However, in some implementations, each AP110 may transmit trigger requests and receive feedback information in parallel (such as using OFDMA, MIMO, etc.).

Based on the received channel feedback information, the APs 110a-110c may perform beamforming (such as by deriving steering matrices) and transmit data to the

user terminals

120a and 120 c. In some implementations, the APs 110a-110c may transmit data after the sounding phase at a particular TTI, or in some implementations, the AP110a may send a trigger frame to indicate the TTI and coordinate data transmission. As discussed, NDPs from multiple APs 110 may be synchronized over the backhaul or pre-corrected based on received NDPAs. Accordingly, in some implementations, for distributed MU-MIMO data transmission to the

user terminals

120a and 120c, the AP110 may utilize the same frequency and time synchronization as used for NDP to ensure proper beamforming. In some implementations, the transmit power backoff used by each AP may be kept constant between the NDP of each AP and the data transmission to ensure proper beamforming (such as to prevent phase rotation).

In some implementations, the NDP transmitted from each AP110 a-110c may carry the same preamble for all APs 110a-110 c. Such preambles may be used by legacy devices that do not support distributed MU-MIMO to defer transmissions.

In some implementations, different APs 110 may have different local oscillators. Thus, when the APs 110 transmit the NDP, there may be a phase drift between them. Accordingly, in order for the user terminals 120 to determine when to listen to the NDP, they may need to track the phase drift of each AP 110. In some implementations, if FDM is used to multiplex transmissions from APs, phase tracking of different APs may be performed by tracking pilots transmitted on different tones for different APs. In some implementations, if TDM is used to multiplex transmissions from APs, rather than transmitting symbols for one AP consecutively, symbol transmissions for different APs may be interleaved for better phase tracking (such as phase drift may change at different times, so it may be beneficial to track drift over a longer period of time for each AP).

In some implementations, if transmissions from APs are multiplexed using a P matrix, non-overlapping tones may be assigned for transmission by different APs for phase tracking. Alternatively, multi-stream pilots may be used, where one stream per AP is transmitted on the pilot tones to track the phase of each AP, or where the number of streams transmitted on the pilot tones per AP is equal to the number of streams given to the AP for transmitting LTFs.

Fig. 6 illustrates a signal diagram of an example sequential sounding procedure for distributed MU-MIMO. In some implementations, initially, any of the APs (here shown as AP110 a) transmit the NDPA as described with respect to fig. 5. The AP110a then transmits the NDP separately to the

user terminals

120a and 120 c. As discussed, the AP110a then transmits one or more trigger requests to the

user terminals

120a and 120c requesting feedback. The

user terminals

120a and 120c then transmit the channel feedback information to the AP110a either serially or in parallel. After the

user terminals

120a and 120c transmit channel feedback information to the AP110a, the AP110b separately transmits an NDP to the

user terminals

120a and 120c, transmits one or more trigger requests requesting feedback, and receives the channel feedback information. Accordingly, a single NDPA is transmitted for starting a sounding procedure for multiple APs, but the NDPs are sequentially transmitted.

In some implementations, although not shown, for a sequential sounding procedure, instead of one AP110 transmitting one NDPA for multiple NDPs transmitted by multiple APs 110, each AP110 may sequentially transmit an NDPA and perform a sounding procedure. Accordingly, each AP110 transmits its own NDPA (such as shown in fig. 6) before sequentially transmitting NDPs.

In both sequential sounding procedures, the NDPA may still identify user terminals associated with APs other than the transmitting AP, and the NDPA may thus identify user terminals in the BSS of the transmitting AP and the OBSS of the transmitting AP. Further, the trigger request sent from the transmitting AP may still identify user terminals associated with other APs, and the trigger request may thus identify user terminals in the BSS of the transmitting AP and the OBSS of the transmitting AP.

In some implementations, the transmit power backoff used by each AP may be kept constant between the NDP of each AP and the data transmission to ensure proper beamforming (such as to prevent phase rotation). Further, in some implementations, for the sequential sounding schedule, the RxAGC at the user terminal may be held constant between when one AP is sounding and when another AP is sounding to prevent gain drift. In some implementations, NDPA may (such as implicitly) indicate to the user terminal to keep the RxAGC constant.

As discussed, in distributed MU-MIMO, multiple APs 110 may coordinate beamforming. To this end, in some implementations, groups of APs 110 are formed to perform distributed MU-MIMO. In some implementations, a group of APs 110 may be formed by exchanging information over the backhaul. In some implementations, a group of APs 110 may be formed by exchanging information over the air. For example, one AP110 may invite other APs 110 to join a distributed MU-MIMO transmission and exchange frames with other APs 110 to form a group.

Initially, AP110 (AP 110a in this example) transmits a group formation trigger. For example, if AP110a is scheduled for DL MU-MIMO transmission and is not transmitting using all available spatial streams at AP110a, AP110a may transmit a group formation trigger so that the remaining spatial streams can be used by other APs 110. The group formation trigger may include the number of streams AP110a has available for additional transmissions.

Neighboring APs of AP110a (APs 110b and 110c in this example) may receive the group formation trigger and determine whether they will join AP110a in a distributed MU-MIMO transmission. For example, any neighboring AP with data to transmit may determine to join the group with AP110 a. For the neighboring APs 110b and 110c, which determine to join the group, each communicate an intent to participate to the AP110 a. The intent to participate may include, for example, a list of user terminals 120 to which a given AP110 wishes to transmit data in a distributed MU-MIMO transmission. Further, the intent to participate may include, for example, the number of spatial streams desired for transmission per user terminal. In some implementations, the AP110 transmits the intent to participate in parallel using open-loop MU-MIMO (similar to uplink MU-MIMO) or using UL-OFDMA.

The AP110a may receive the intent to participate, determine the group, and perform a sounding phase and distributed MU-MIMO transmission, such as utilizing the techniques described herein. In some implementations, if the AP110 receives an intent to participate requesting more spatial streams than the AP110a has available, the AP110a may select which APs to include in the group and which streams to assign to which APs.

In some implementations, the AP110a may transmit the final group configuration before performing the sounding phase and after the AP110a receives the intent to participate. The final group configuration may include a list of APs 110 included in the group. Further, in some implementations, the final group configuration indicates which spatial streams are assigned to which APs 110 (such as by mapping an AP identifier to a stream index). In some implementations, the final group configuration may include a list of user terminals 120 (such as identifiers of the user terminals 120) to which the group of APs 110 will send the distributed transmission. Furthermore, in some implementations, the final group configuration indicates which spatial streams or how many spatial streams are assigned to which user terminals 120 (such as by mapping user terminal identifiers to stream indices). In some implementations, instead of the AP110a sending the final group configuration, this information is included in the NDPA, as discussed in the sounding phase.

Fig. 8 illustrates example operations 800 for performing a sounding procedure for distributed MU-MIMO in accordance with some implementations of the present disclosure. According to some implementations, operation 800 may be performed by an access point (such as access point 110).

At 802, a first access point of a plurality of access points transmits an announcement frame (such as NDPA) for performing a beamforming procedure for a distributed transmission (such as distributed MU-MIMO). In some implementations, the distributed transmission includes transmissions from the plurality of access points. In some implementations, the announcement frame includes at least one identifier of a user terminal in a basic service set different from a basic service set of the first access point.

At 804, the first access point transmits packets (such as NDPs) for measuring a channel to one or more user terminals. At 806, the first access point receives feedback information from the user terminal (and the other one or more user terminals) based on the packet for measuring channels.

At 808, the first access point transmits the distributed transmission using the beamforming procedure (such as the plurality of access points transmitting the distributed transmission). The beamforming procedure is based on the feedback information.

Fig. 9 illustrates example operations 900 for performing an over-the-air group formation procedure for distributed MU-MIMO according to some implementations of the present disclosure. According to some implementations, operation 900 may be performed by an access point (such as access point 110).

At 902, a first access point transmits a group formation trigger for forming a group comprising a plurality of access points for performing a beamforming procedure for distributed transmission (such as distributed MU-MIMO). At 904, the first access point receives an intent to participate from at least one of the plurality of access points based on the group formation trigger. At 906, the first access point forms the group based on receiving the intent to participate from the at least one of the plurality of access points.

The various operations of the methods described above may be performed by any suitable means capable of performing the corresponding functions. The apparatus may include various hardware and software components and modules, including but not limited to a circuit, an Application Specific Integrated Circuit (ASIC), or a processor. Generally, where operations are illustrated in the figures, those operations may be performed by any suitable respective counterpart means plus functional components.

According to some implementations, such means may be implemented by a processing system configured to perform the respective functions by implementing the various algorithms described above, such as in hardware or by executing software instructions.

For example, the means for determining and the means for scheduling may include one or more processors (such as RX data processors 242 and 270, controllers 230 and 280, and TX data processors 210, 288) of AP110 or user terminal 120 illustrated in fig. 2. Additionally, the means for transmitting and the means for receiving may include one or more of a transmitter/receiver (such as one or more of transceivers TX/RX 222 and 254) or one or more antennas (such as one or more of antennas 224 and 252).

As used herein, a phrase referring to "at least one of" a list of items refers to any combination of these items, including a single member. As an example, "at least one of a, b, or c" is intended to encompass: a. b, c, a-b, a-c, b-c, and a-b-c.

The various illustrative logics, logical blocks, modules, circuits, and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. This interchangeability of hardware and software has been described generally, in terms of its functionality, and is illustrated in the various illustrative components, blocks, modules, circuits, and processes described above. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

The hardware and data processing apparatus used to implement the various illustrative logics, logical blocks, modules, and circuits described in connection with the implementations disclosed herein may be implemented or performed with a general purpose single-or multi-chip processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. In some implementations, certain processes and methods may be performed by circuitry that is dedicated to a given function.

In one or more implementations, the functions described may be implemented in hardware, digital electronic circuitry, computer software, firmware (including the structures disclosed in this specification and their structural equivalents), or any combination thereof. Implementations of the subject matter described in this specification can also be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on a computer storage medium for execution by, or to control the operation of, data processing apparatus.

If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. The processes of the methods or algorithms disclosed herein may be implemented in processor-executable software modules, which may reside on computer-readable media. Computer-readable media includes both computer storage media and communication media, including any medium that can be implemented to transfer a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Any connection is properly termed a computer-readable medium. Disk (disk) and disc (disc), as used herein, includes Compact Disc (CD), laser disc, optical disc, digital Versatile Disc (DVD), floppy disk and blu-ray disc where disks (disks) usually reproduce data magnetically, while discs (discs) reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or set of codes and instructions on a machine readable medium and computer readable medium, which may be incorporated into a computer program product.

Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of the disclosure. Thus, the claims are not intended to be limited to the implementations shown herein but are to be accorded the widest scope consistent with the present disclosure, the principles and novel features disclosed herein.

In addition, those of ordinary skill in the art will readily appreciate that the terms "upper" and "lower" are sometimes used for ease of describing the drawings and indicate relative positions corresponding to the orientation of the drawings on a properly oriented page and may not reflect the true orientation of any device as implemented.

Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination, or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Further, the figures may schematically depict one or more example processes in the form of a flow diagram. However, other operations not depicted may be incorporated into the schematically illustrated example process. For example, one or more additional operations may be performed before, after, concurrently with, or between any of the illustrated operations. In some environments, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

Claims

1. A method of wireless communication at a first access point, comprising:

transmitting, to a plurality of access points, a group formation trigger for forming a group comprising one or more of the plurality of access points;

receiving an intent to participate from at least a second access point of the plurality of access points based on the group formation trigger;

based on the intent to participate, forming the group comprising the first access point and at least the second access point, wherein forming the group comprises transmitting a group configuration to at least the second access point; and

transmitting a distributed transmission using a beamforming procedure, wherein the distributed transmission comprises a transmission from the first access point and a transmission from at least the second access point.

2. The method of claim 1, further comprising:

assigning a spatial stream on which at least the second access point of the group will transmit packets for measuring channels to at least the second access point of the group; and

transmitting an announcement frame to a user terminal and at least the second access point of the group for performing the beamforming procedure for the distributed transmission, wherein the announcement frame comprises the spatial stream allocations.

3. The method of claim 2, further comprising:

transmitting a packet for measuring the channel to the user terminal during a Transmission Time Interval (TTI) after transmitting the announcement frame, wherein the packet for measuring the channel is configured to cause the user terminal to transmit feedback information based on the packet for measuring the channel; and

receiving feedback information from the user terminal based on the packet for measuring the channel, wherein the beamforming procedure is based on the feedback information.

4. The method of claim 3, wherein the announcement frame is configured such that each access point in the group transmits the packets for measuring the channel during the TTI after receiving the announcement frame.

5. The method of claim 1, further comprising receiving an announcement frame transmitted by the second access point to the group.

6. The method of claim 5, further comprising:

transmitting, to a user terminal, a packet for measuring a channel after receiving the announcement frame, wherein the packet for measuring the channel is transmitted on a same Transmission Time Interval (TTI) as another packet for measuring another channel transmitted by a respective one or more access points in the group, wherein the packet for measuring the channel is configured to cause the user terminal to transmit feedback information based on the packet for measuring the channel; and

7. A first access point of a plurality of access points, comprising:

a transceiver;

a memory comprising instructions; and

a processor configured to execute the instructions to cause the first access point to:

transmitting, via the transceiver, a group formation trigger for forming a group comprising one or more of the plurality of access points;

receiving, via the transceiver, an intent to participate from at least a second access point of the plurality of access points based on the group formation trigger; and

forming the group comprising the first access point and at least the second access point of the plurality of access points based on the intent to participate, wherein the instructions that cause the first access point to form the group comprise instructions that cause the first access point to transmit a group configuration to at least the second access point via the transceiver; and

transmitting, via the transceiver, a distributed transmission using a beamforming procedure, wherein the distributed transmission comprises a transmission from the first access point and a transmission from at least the second access point of the plurality of access points.

8. The first access point of claim 7, wherein the processor is further configured to execute the instructions to cause the first access point to:

transmitting, via the transceiver, an announcement frame to a user terminal and at least the second access point of the group for performing the beamforming procedure for the distributed transmission, wherein the announcement frame comprises the spatial stream allocation.

9. The first access point of claim 8, wherein the processor is further configured to execute the instructions to cause the first access point to:

transmitting, via the transceiver, a packet for measuring the channel to a user terminal during a Transmission Time Interval (TTI) after transmitting the announcement frame, wherein the packet for measuring the channel is configured to cause the user terminal to transmit feedback information based on the packet for measuring the channel; and

receiving, via the transceiver, feedback information from the user terminal based on the packet for measuring the channel, wherein the beamforming procedure is based on the feedback information.

10. The first access point of claim 9, wherein the announcement frame is configured such that each access point in the group transmits the packets for measuring the channel during the TTI after receiving the announcement frame.

11. The first access point of claim 7, wherein the processor is further configured to execute the instructions to cause the first access point to receive, via the transceiver, an announcement frame transmitted by the second access point to the group.

12. The first access point of claim 11, wherein the processor is further configured to execute the instructions to cause the first access point to:

transmitting, via the transceiver, a packet to a user terminal for measuring a channel after receiving the announcement frame, wherein the packet for measuring the channel is transmitted on a same Transmission Time Interval (TTI) as another packet for measuring another channel transmitted by the respective one or more access points in the group, wherein the packet for measuring the channel is configured to cause the user terminal to transmit feedback information based on the packet for measuring the channel; and

13. A first access point of a plurality of access points, comprising:

means for transmitting a group formation trigger for forming a group comprising one or more access points of the plurality of access points;

means for receiving an intent to participate from at least a second access point of the plurality of access points based on the group formation trigger;

means for forming the group including the first access point and at least the second access point of the plurality of access points based on the intent to participate, wherein the means for forming the group includes means for transmitting a group configuration to at least the second access point; and

means for transmitting a distributed transmission using a beamforming procedure, wherein the distributed transmission comprises a transmission from the first access point and a transmission from at least the second access point of the plurality of access points.

14. The first access point of claim 13, further comprising:

means for assigning a spatial stream on which at least the second access point of the group will transmit packets for measuring channels to at least the second access point of the group; and

means for transmitting an announcement frame to a user terminal and at least the second access point of the group for performing the beamforming procedure for the distributed transmission, wherein the announcement frame comprises the spatial stream allocations.

15. The first access point of claim 14, further comprising:

means for transmitting a packet for measuring the channel to the user terminal during a Transmission Time Interval (TTI) after transmitting the announcement frame, wherein the packet for measuring the channel is configured to cause the user terminal to transmit feedback information based on the packet for measuring the channel; and

means for receiving feedback information from the user terminal based on the packet for measuring the channel, wherein the beamforming procedure is based on the feedback information.

16. The first access point of claim 15, wherein the announcement frame is configured such that each access point in the group transmits the packets for measuring the channel during the TTI after receiving the announcement frame.

17. The first access point of claim 13, further comprising means for receiving an announcement frame transmitted by the second access point to the group.

18. The first access point of claim 17, further comprising:

means for transmitting a packet to a user terminal for measuring a channel after receiving the announcement frame, wherein the packet for measuring the channel is transmitted on a same Transmission Time Interval (TTI) as another packet for measuring another channel transmitted by a respective one or more access points in the group, wherein the packet for measuring the channel is configured to cause the user terminal to transmit feedback information based on the packet for measuring the channel; and

19. A non-transitory computer-readable medium having instructions stored thereon, which, when executed by a first access point of a plurality of access points, cause the first access point to perform operations comprising:

transmitting a group formation trigger for forming a group comprising one or more access points of the plurality of access points;

based on the intent to participate, forming the group comprising the first access point and at least the second access point of the plurality of access points, wherein forming the group comprises transmitting a group configuration to at least the second access point; and

transmitting a distributed transmission using a beamforming procedure, wherein the distributed transmission comprises a transmission from the first access point and a transmission from at least the second access point of the plurality of access points.

20. The non-transitory computer-readable medium of claim 19, wherein the operations further comprise:

21. The non-transitory computer-readable medium of claim 20, wherein the operations further comprise:

22. The non-transitory computer-readable medium of claim 21, wherein the announcement frame is configured to cause each access point in the group to transmit the packet for measuring the channel during the TTI after receiving the announcement frame.

23. The non-transitory computer-readable medium of claim 19, wherein the operations further comprise receiving an announcement frame transmitted by the second access point to the group.

24. The non-transitory computer-readable medium of claim 23, wherein the operations further comprise: